325 



Atlantic Océan, but the shells of the two species can be very easily distinguished. The sub- 

 generic position of thèse forms is far from clear. 



Genus Lyonsiella M. Sars. 



1869. Lyonsiella Sars, M., Vid. Selskab. Forhandl., p. 257. 



1885. Lyonsiella Smith, "Challenger" Lamellibranchia, p. 73. 



1887. L^yonsiella Fischer, P., Man. ConchylioL, p. 116. 



1903. Lyonsiella Dali, Trans. Wagner Free Inst. Sci. Philadelphia, III, p. 15 10. 



M. Sars only introduced the name in 1869, and it was not till 1872 ^) that a description 

 of the shell and animal was published by G. O. Sars from the notes left by M. Sars. In this 

 latter work the author considered Lyonsiella to by only synonymous with Pecchiolia Meneghini, 

 but I agrée with Fischer and Smith that Lyonsiella is a good genus, quite distinct from 

 Pecchiolia. The génotype is Lyonsiella abyssicola Sars, and a good définition of it is published 

 by Fischer (loc. cit., p. 1162). 



1. Lyonsiella pilula sp. nov. (Plate VII, figs. 23, 24). 



Lyonsiella pilula is very closely allied to L. papyracea Smith ^) from "Challenger" St. 157, 

 about iioo miles south-west of Australia. The shell of L. pilula is, however, very much 

 smaller, thinner, almost transparent, globose, much more swoUen and subequilateral. The umbones 

 are more prominent and are turned inwards and forwards. The posterior dorsal margin is more 

 oblique and the sculpture consists of about 30 hair-like, radial lines ; no concentric sculpture 

 can be distinguished on the surface of the valves. 



Measurements of the Holotype : — Length 5.8 mm., height 6.2 mm., diameter 5.2 mm. 



Habitat: — The unique Holotype was brought up in a deep-sea trawl at St. 88 

 (o°34^6N., ii9°8'.5E., 1301 mètres). 



2. Lyonsiella smithi sp. nov. (Plate VII, figs. 25, 26). 



Lyonsiella smithi is closely allied to L. jeffreysii Smith ^) from the mid-Atlantic but the 

 shell of the new species is very much smaller, much thinner, less inflated and relatively more 

 elongated. The posterior dorsal margin is much longer and more oblique, and forms the upper 

 outline of the beak-like posterior part of the shell. The ventral margin is less arcuate, but 

 behind the middle it curves up suddenly. The sculpture consists of a number of very regular, 

 radial lines and only a few concentric striae ; in addition the surface is finely granular. 



Measurements of Holotype: — Length 9mm., height 8.5 mm., diameter 6.6mm. 



Habitat : — The unique Holotype of the species was brought up in a deep-sea trawl 

 at St. 178 (2° 40' S., i28°37'.5E., 835 mètres). 



I hâve great pleasure in dedicating this new species to the memory of the late Mr. Edgar 

 A. Smith, of the British Muséum (Nat. Hist.). London to whom we owe the greater part of 

 our information in référence to this interesting genus of bivalves. 



1) Saks, G. O. — Remarkable Forms of Animal Life, p. 25 (Christiana, 1872^. 



2) Smith, E. A. — "Challenger" Lamellibranchia, p. 73, pi. XXV, figs. 2, 2(7,^ (1885). 



3) Smith, E. A. — "Challenger" Lamellibranchia, p. 73, pi. XXV, figs. l, ifl, iJ (1885J. 



